Disclosed herein is an image conditioning coating, and more particularly disclosed is a contact leveling coating for a contact leveling member in a printing device. The contact leveling coating can be used with imaging materials including ultraviolet (UV) curable gel inks to provide offset-free, robust, and reliable image conditioning and to provide improved reliability of print engine components. In a specific embodiment, a contact leveling coating for a direct to paper ink jet imaging member is disclosed. In another specific embodiment, a contact leveling coating for use with UV curable gel inks is disclosed.
Ink jet printing systems commonly use either a direct printing architecture or an offset printing architecture. In a typical direct printing system, ink is ejected from jets in the printhead directly onto the final receiving web or substrate such as paper. In an offset printing system, the image is formed on an intermediate transfer surface and subsequently transferred to the final receiving substrate such as a web or individual substrate such as paper.
UV curable gel inks are in the gel phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of ink drops. UV curable gel ink is typically jetted at a temperature of about 75° C. and has a melt viscosity at jetting temperature of about 10 centipoise.
Phase change inks such as UV curable gel inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
However, gel inks require some type of transformation such as curing to prevent them from running or smearing when printed onto a substrate and subjected to general handling. In addition, uncured gel inks stick to roller surfaces in print paths, making them unsuitable for many printing applications without some sort of transformation or curing. There is a desire to have the ink leveled prior to having it UV cured. The reason for this is so that gloss is more uniform, missing jets can be masked, and certain applications such as packaging require thin layers of relatively constant thickness. Since these inks have a mayonnaise consistency, they have very little cohesive strength prior to curing. In addition, gel inks are typically designed to have good affinity to many materials. This means that conventional methods for flattening a layer of ink tend to fail, because the ink splits and leaves much of the image behind on the device trying to flatten it, such as a traditional fuser roll typically used in xerography. The present description proposes a way to resolve this issue.
Direct to paper as-is printed images can require image conditioning (leveling) to improve image quality and gloss. FIG. 1 illustrates a simplified ink jet printing system 100 wherein a printhead nozzle 102 jets ink droplet 104 directly to a final receiving substrate such as paper 108 to form printed image droplet 106 on the paper 108. Due to surface energy profiles, the jetted ink drops bead up on the surface of paper, resulting in a contact angle between the printed droplet 106 and the paper 108 as indicated by arrows 110, 111, 112, wherein γ1(T) is the surface tension of the ink, γ2(T) is the surface tension of the paper, γ12(T) is the interfacial tension between the paper 108 and the ink 106, wherein the force balance in the plane of paper is→γ1 cos θ+γ12=γ2; and→cos θ=(γ2−γ12)/γ1(T).
Contact angle pinning, along with the presence of intermittent missing and weak jets, can lead to non-uniform streaky ink profiles resulting in low image quality and low image gloss. Several approaches have been proposed to condition a printed image, such as non contact techniques including thermal reflow, air knife shearing, modifying the ink formulation to achieve a 120 micrometer line width, and contact leveling techniques.
U.S. Patent Publication 20090141110, published Jun. 4, 2009, which is hereby incorporated by reference herein in its entirety, discloses a printing apparatus, including a) a printing station with at least one printhead for applying phase change ink to a substrate in a phase-change ink image, and b) an ink spreading station including a heated or unheated ink spreading member and a back-up pressure member in pressure contact with the ink spreading member, and wherein a nip is formed between the ink spreading member and the back-up pressure member for spreading the phase change ink image on the substrate, wherein said substrate is passed through the nip, and wherein the pressure member includes i) a substrate, and ii) an outer coating having a polymer matrix with an oleophobic resin, a fluoropolymer lubricant, and a first additive.
U.S. Patent Publication 20090142112, published Jun. 4, 2009, which is hereby incorporated by reference herein in its entirety, discloses an offset printing apparatus for transferring and optionally fixing a phase change ink onto a print medium including a) a phase change ink application component for applying a phase change ink in a phase change ink image to an imaging member; b) an imaging member for accepting, transferring and optionally fixing the phase change ink image to the print medium, the imaging member having: i) an imaging substrate, and thereover ii) an outer coating comprising a polymer matrix with an oleophobic resin, a fluoropolymer lubricant, and a first additive, and c) a release agent management system for supplying a release agent to the imaging member wherein an amount of release agent needed for transfer and optionally fixing the phase change ink image is reduced.
While currently available image conditioning methods and devices are suitable for their intended purposes, a need remains for an improved image conditioning surface that can contact an image and level the image while remaining ink-phobic enough to prevent offset to the contact leveling surface. There further remains a need for improved image conditioning that provides improved image quality, image gloss, and that compensates for missing or weak jets. There further remains a need for a contact leveling coating that provides green, robust, and reliable image conditioning for ultra-violet curable gel ink print engines. There further remains a need for a contact leveling coating that is wear resistant, thermally stable when heated to operating temperature, has consistent mechanical properties under high load, resists adhesion of ink, and is oleophobic.
The appropriate components and process aspects of the each of the foregoing U.S. Patents and Patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.